The invention relates generally to hydraulically fed food cutting (“hydro-cutting”) apparatuses, and more particularly to a tube assembly used in a hydro-cutting apparatus to cut food products into a plurality of smaller pieces.
Many food products, particularly vegetables and fruits, are processed prior to sale to preserve the food so it is safe and appealing at the time of consumption. The processing can be by canning or freezing, among others. Furthermore, unless it is an edible size before processing, most food products must be sliced or otherwise shaped into an edible size prior to the preservation process. Slicing and shaping operations have been accomplished traditionally with sharpened blades. Such blades can be hand-held, but hand-held knives are relatively slow and dangerous to the person using them. Other blades are machine-driven and other machines for cutting drive the food products at high speed into a stationary or machine-driven blade. Food cutting machines increase the rate and consistency of slicing, and provide a higher degree of safety in the food slicing industry.
Recent advances in food product cutting technologies have resulted in the hydraulically fed cutting apparatus. The driving force used in this system is moving water, and thus the process is called “hydraulic cutting”, which is referred to by the shorthand term “hydro-cutting”. Hydro-cutting involves the propulsion of water and food products, typically at very high speed, through a path that includes a stationary cutting blade. In the vegetable and fruit cutting industry, food products are sliced along the longitudinal axis (e.g., French fries) and along the transverse axis (e.g., potato chips). Production cutting systems and related knife fixtures are generally well known in the art of hydro-cutting vegetable products. Typical hydro-cutting systems have a knife fixture that is mounted at a position along the path of the food product to slice parallel to the flow of water. Such parallel cutters usually cut or slice into strips or into a helical shape. In such a system, the food products are conveyed one-at-a-time in single file succession into the stationary cutting blades with enough kinetic energy to carry the product through the stationary knife fixture.
Hydraulic food cutters are used to cut a wide variety of food products, including potatoes, beets, zucchini, cucumbers, and others. Cutting potatoes has been the most common application of hydro-cutting machines. However, it should be understood that these hydraulic food cutters are capable of cutting, and are used to cut, a wide variety of food products.
The basic configuration of a prior art system is shown, in schematic format, in FIG. 1. In such a typical prior art hydraulic cutting apparatus, where potatoes are to be cut, the potatoes are dropped into a tank 10 filled with water and then pumped through conduit into an alignment chute or tube 12 wherein the potatoes are aligned and accelerated to high speed before impinging upon a fixed array of cutter blades where the potato is cut into a plurality of smaller pieces.
The tank filled with water, which is one of the components of a prior art hydraulic cutting apparatus for use in cutting potatoes, is referred to as a receiving tank 10. Peeled or unpeeled potatoes are dropped into the receiving tank and a food pump 13, typically a single impeller centrifugal pump, is provided to drive the potatoes through the system. The pump draws water from the receiving tank and pumps the water and the suspended potatoes from the tank into the accelerating tube 12, which functions as the converging portion of a venturi. The accelerator tube is used to accelerate and align the potatoes immediately prior to impinging upon the stationary knife blades of the cutter blade assembly 14.
The use of an accelerator tube is required in order to perform two functions. First, the accelerator tube accelerates the water and food product to the velocity required in order for it to pass cleanly through the knife blade assembly. Secondly, the accelerator tube aligns and centers the food products prior to impingement upon the knife blade assembly. In the case of potatoes, a common velocity range is from about 40 to about 60 feet per second. The hydro tube is a tapered bore pipe that accomplishes this alignment. Prior art machines that use hydro tubes commonly have rigid tubes lined with flexible material.
Each whole potato impinging upon the knife blade assembly passes through the cutting blade array and is thereby cut into a plurality of food pieces, for example French fry pieces. These pieces pass with the water into the second half of the venturi which is a diverging tube 15 in which the water and the cut food pieces are decelerated back to a slower velocity. The water and cut food pieces are then deposited onto a dewatering conveyer chain 16. The water passes through the dewatering conveyor chain and is collected and recycled back to the receiving tank. The cut food pieces remain on the conveyor chain and are carried off for further processing.
During the cutting process, as the potato approaches the cutting knives, the potato needs to be aligned with the central axis of the knife set. This alignment maximizes finished product yield. In the past, significant effort has been directed toward the development of good alignment or acceleration tubes that can properly align and accelerate the whole food product so that each whole food product is properly centered relative to the cutter blade array prior to impinging upon it. An example of these efforts can be seen in U.S. Pat. No. 4,614,141, which teaches an alignment tube assembly used to accelerate and align whole potatoes immediately prior to impinging upon a cutter head array. Other patents of interest include U.S. Pat. Nos. 5,568,755 and 5,806,397, both of which, along with U.S. Pat. No. 4,614,141, are hereby incorporated by reference.
In the prior art, the alignment (accelerator) tube is usually a two-part assembly consisting of a converging, conically-shaped metal or other rigid material housing, into which is inserted a more resilient liner, which liner is usually formed of reinforced food grade rubber that seats against the inner surface of the rigid housing. In the prior art, the larger inlet end of the tapered housing is hard-plumbed to the discharge line of the centrifugal pump. Usually this is a bolted connection between a flange on the discharge line and a flange formed integrally to the input end of the tapered housing.
At the outlet end of the tapered accelerator housing, the resilient liner usually extends out a few inches and this protruding portion is inserted into the inlet hole of the cutter blade housing. In some prior art designs the outlet of the accelerator tube liner (the tip of the protruding portion) ends immediately in front of the knife blade array. A water seal between the cutter blade housing and the accelerator tube assembly can be made by hard-plumbing the accelerator tube housing to the cutter blade housing. However, this hard plumbing is not done in all designs because it is too difficult and time-consuming to remove the housing for repair and maintenance.
Since the interface region between the accelerator tube assembly and the cutter blade housing is the narrowest part of the venturi, the hydraulic pressure at that point in the system is greatly increased from that found at the discharge of the pump, usually in the range of two to ten pounds per square inch. Instead of hard plumbing the outlet of the accelerator tube assembly to the inlet of the cutter blade housing, multiple packing rings are used. This is done to reduce the time required to disassemble and remove the accelerator tube assembly from the system. Each time the outlet end of the accelerator tube liner is removed from the inlet of the cutter blade housing, the packing rings should be replaced.
Accelerator tube assemblies must be periodically disassembled for many reasons that include cleaning, replacement of worn out liners, replacement of the liner with a different size liner, and cleaning out a “plug” of uncut food product. All but the last are usually handled as scheduled maintenance items, and the time requirements, while significant, are not critical. The unscheduled and unwanted plug-up of the system is a problem because it often results in a complete shutdown of a production line without prior notice.
In the case of potatoes, production rates for hydraulic cutting systems are typically between 20,000 pounds to 35,000 pounds per hour. At a cutting rate of 20,000 pounds per hour, and assuming an average potato weight of ten ounces, the number of potatoes passing through the cutter blade assembly is approximately 32,000 potatoes per hour, or approximately 8.8 potatoes per second. If one potato plugs the cutter blade assembly, in 10 seconds there will be 88 potatoes backed up behind the cutter housing in the accelerator tube assembly; in 20 seconds, 176 potatoes. At 35,000 pounds per hour the problem is further aggravated. In practice, if a prior art hydraulic cutting apparatus plugs while unattended, it is not uncommon for the plug to include potatoes backed up into the food pump. A plug such as this can take hours to clean out since it requires substantial disassembly of the machine and its attendant piping. As a result, it is common practice in food processing plants to provide operating personnel to continuously monitor the operation of the hydro-cutting system.
The need exists for an acceleration tube that accommodates food products that vary in size without plugging.